1. Technical Field
This invention relates to brakes used on heavy vehicles such as aircraft, trucks, trains, and, more particularly, to a structural fiber reinforced ceramic matrix composite material adapted for high temperature brake use for the entirety of components of a brake system or as brake pads which can be used in the normal manner for brake pads. It also relates to a method of integrally molding fiber reinforced ceramic matrix composite brake components and attaching them to the surfaces of metal brake parts.
2. Background Art
Any vehicle that moves typically is provided with a brake system with which to stop it. The lighter the combined stopping weight, the fewer the problems involved in designing a brake system which will last for an extended period of time and then be easy and inexpensive to replace or renovate. Thus, a vehicle such as a bicycle can be fitted with small rubber pads that squeeze and grip the rims of the wheels which will last virtually forever and which can be replaced in a few minutes at little expense.
When one gets to the mass of an automobile, which may contain a number of passengers, frictional heat build-up during stopping becomes a problem to be considered. Most automobiles today employ a so-called caliper disk brake on at least the front wheels since during stopping the weight of the vehicle is moved forward to the front wheels due to the force of inertia. Disk brakes as depicted in FIG. 1 have good stopping power for various reasons. A rotor 10 carries the wheel (not shown) on a shaft 12. As the wheel rotates, the rotor 10 rotates in combination with it. The rotor 10 is disposed between a pair of calipers 14 having brake pads 16 thereon. To stop the automobile, hydraulic pressure is used to move the calipers 14 together until the rotor 10 is squeezed under pressure between the pads 16. The calipers 14 are attached to the frame of the automobile and cannot rotate. The pads 16 are of a high friction material that resists deterioration and wear under fairly high temperature conditions. Thus, when the rotor 10 is squeezed by the calipers 14, a high frictional stopping force is applied to the rotor 10, bringing the automobile to a stop. Since the pads 16 are flat and contact the flat sides of the rotor 10, the entire area of the pads 16 contacts the rotor 10 to impart the stopping forces. This is in contrast to so-called "drum" brakes wherein the shoe carrying the pad is a circular arc which is supposed to match and fit the inside of a cylindrical brake drum. If there is a mismatch, only small parts of the pad actually rub on the drum. And, if there is a lot of frictional force generating a lot of frictional heat, the drum can be warped out of shape from the heat. With the disk brake, by contrast, the rotor 10 is in the air stream passing under the automobile, is thicker, and is therefore usually able to dissipate any heat build-up that takes place. And, even if minor warping should take place, the calipers are usually in a floating mounting that can follow the resultant wobble of the rotor.
To further prevent any damage to the surface of the rotor 10, the prior art suggests facing the rotor 10 with a monolithic ceramic coating 18, which may or may not work for its intended purpose within the environment of an automobile. It definitely would not work for a braking system environment such as that addressed by the present invention.
When it comes to stopping an airplane, the braking system is an entirely different story. Particularly with a so-called "jumbo" jet carrying hundreds of passengers plus their baggage and freight in addition to the weight of the airplane itself, designing a successful braking system is a major undertaking. The prior art is depicted in FIG. 3 in simplified form. There are a plurality of rotors 10' carrying shafts 12 which, in turn, carry the wheels (not shown) of the airplane. The rotors 10' are stacked with a plurality of stators 20 into a stack 22. While only two rotors 10' are shown, it is for simplicity only and many rotors 10' and stators 20 may be in the stack 22 of a typical airplane brake. The stack 22 is disposed between pairs of wheels. The stators 20 are fixed and do not rotate while the rotors 10' rotate in combination with the wheels. To apply the brake and stop the airplane, hydraulic pressure is applied which causes the stack 22 to be compressed together thereby squeezing the rotating rotors 10' between the fixed stators 20.
With smaller aircraft, the above-described brake construction was not a problem and worked well for its intended purpose. With the advent of large jets (both commercial and military) the frictional forces and attendant heat build-up soon became a major factor. This is particularly true with an aborted take-off with non-normal braking, which can result in the complete destruction of the entire brake stack 22. Modern jet brakes are of three types--all steel (rotors and pads), or steel rotors with sintered pads, and carbon/carbon rotors and pads. With an all steel brake system, both the stators 20 and rotors 10' are made of high quality steel specifically designed for the purpose. The steel/steel brakes develop good internal frictional forces. This is necessary in order to stop the airplane. If friction is removed, there is no heat build-up; but, there is also no stopping force created. Under the conditions of a normal stop, the brakes are applied in such a manner that they can dissipate the heat generated before it becomes a problem. Also, the so-called "jet brake" created by reversing the thrust of the jet engines is used to slow the airplane so that the brakes do not have to do all the work. The airplane is never brought completely to a stop from landing speed so that the rotors 10' and stators 20 are separated in the stack 22 as the heat created in them from frictional forces is dissipated.
In an aborted take-off, the airplane has attained a high ground speed which may be close to that required for take-off. At the last moment, the decision is made to abort, i.e. cancel the take-off. The only thing available to bring the airplane to a complete stop before the end of the runway is the brakes. To accomplish this, the pilot must "stand on" the brakes, i.e. fully apply them and hold them until the plane stops. The result is a heat build-up that cannot be successfully dissipated in time. The rotors 10' and stators 20--literally become so hot that as soon as the plane stops (or perhaps sooner), they weld together. Moreover, the built up heat travels to the surrounding structure and the wheels and may even start those on fire. If the brakes seize before the airplane stops, the rubber wheels drag instead of rotating thereby quickly wearing through them whereupon they burst, causing the supporting structure to drag on the ground and maybe collapse. In short, it can be something that is going to require extensive repair of the airplane before it will be able to fly again.
To solve the above-describe problem, carbon/carbon brakes were developed and are in use in the prior art. Carbon/carbon brakes have a number of problems--they provide low friction characteristics until they get hot, they are porous and therefore can be contaminated by de-icing or other fluids, they oxidize at a temperature similar to that realized during "heavy Taxing", they generate corrosive dust, and they are very expensive and time consuming to make. The carbon rotors 10' and carbon stators 20 are created by an infiltration process that is very expensive and literally takes weeks to accomplish. The cold stack 22 has a very low coefficient of friction and will not stop the plane. Thus, when first taxiing, the pilot must periodically apply the brakes to cause sufficient heat build-up such that the airplane can be stopped with the brakes when the need arises. Should the is need arise before sufficient friction has built up, the airplane cannot be stopped and a large-scale wreck can occur. Because the problem of break seizure is eliminated, most airlines and the military presently use the carbon/carbon brakes despite their shortcomings.
Truck, train, and racing applications could also utilize a better breaking system providing lighter weight and longer endurance than current technology braking materials.
Wherefore, it is an object of this invention to provide a seizure-resistant stack type brake system for aircraft and the like which is low cost and easily repairable.
It is another object of this invention to provide a seizure-resistant stack type brake system for aircraft and the like which has a high coefficient of friction even when cold.
It is still another object of this invention to provide a seizure-resistant stack type brake system for aircraft and the like which employs brake pads which can be replaced without having to replace the entire stack of rotors and stators.
It is yet another object of the present invention to provide a brake rotor/drum/pad material that is resistant to destruction in any application involving high frictional braking forces and extremely high generated heat.
It is a further object of the present invention to provide a brake rotor material that is resistant to destruction in any application involving high frictional braking forces and extremely high generated heat.
Other objects and benefits of this invention will become apparent from the description which follows hereinafter when read in conjunction with the drawing figures which accompany it.